So Ellie is careful. She doesn't charge into walking, but she slowly considers things, and when she gets them figured out, she takes off.
This video may show why walking might not be the best idea.
In Margaret's defense, I think that she was trying to hug Ellie -- notice how her hands go under Ellie's arms -- but Margaret is oblivious to the effects her hugs can have on people who haven't properly set their feet before receiving one.
In other news, here is proof that Ellie can walk.